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Want to do a quick and dirty design for a gravity fed sprinkler system from a pond.

Hello,
I was hoping someone could steer me in the right direction here. I have a mining permit I working on and it is in a watershed which requires a non point source type of discharge therefore, a sprinkler system can be used for this. The dewatering pipe is a 4" PVC pipe which will be discharging through a series of 1.5" diameter holes. At full volume the discharge will be full flow through the 4" PVC. The pipe flow from the pond elevation to the field we will be spraying is approximately 550 ft away.

I know nothing about sprinkler systems or how many heads I will need so there is no loss in flow capacity of the 4" pvc dewatering pipe.

I am not looking for a guaranteed design from anyone, just some approximate sizes and numbers. I know how to calculate the head lose due to friction and equivalent lengths for the pipes and fittings, etc. But, I do not know what to expect for head loss at the sprinkler head however.

Your elevation difference works out to about 35 psi. That greatly limits what you can achieve. A conventional system with an electric valve feeding pop-up sprinkler heads is probably out of reach, because about 10 psi gets lost from source to heads.

What you can count on operating from a 35 psi supply are impact heads, especially the Rainbird Maxipaw heads, because they can be adjusted for lower operating pressures. That they also function on "dirty" water is a bonus.

I don't 'get' the "1-1/2 inch holes" - is this describing the inlet pipe?

Yes, the "de-watering" structure is a 4" diam PVC stand-pipe that has a series of three holes drilled into it. It has ~5 rows of three holes, between the sediment storage elev and the top of water elev. If the dewatering holed affect the PSI needed, this pipe can be changed and the holes eliminated.

Running sprinkler heads from pond water requires that you screen the water intake, so that the sprinklers don't clog up. An impact head will pass a particle smaller than the nozzle diameter. You could cover the inlet with something akin to window screening. The Maxipaw heads may not use anywhere near as much water as the big brass heads that often are used in distributing water over a drainage field, but they will work at the pressures you have. They will throw about 35 feet, and use 3 gpm with the standard nozzle, and up to 6 gpm with optional larger nozzles.

If you need to move several hundred gallons per minute, you might have to spend money for a pump and big sprinklers.

How many sprinklers could I expect to run, without pumping? I'm looking at a range of ~200 gpm to dewater the pond in 5 days to ~130 gpm to dewater it in 8 days. Therefore, at the 130 gpm, I am looking at 44 of the 3gpm nozzles or 22 of the 6 gpm. Is that too many? I could possibly go to 9 days at ~117gpm. That would be ~39 3gpm or 19 6gpm sprinklers.

Simple economics has you using the largest nozzles. Even at 200 GPM, the long run between pond and drainage field won't sap the operating pressure more than 2 psi. It becomes up to you to arrange the heads and piping in the field so that pressure is maintained. If the 4-inch pipe enters the field at a central location, you might be able to branch out immediately to 4 or 5 or 6 pipes feeding different sections, using 2-inch PVC

I have it configured with a screen at the intake, a valve just outside the pond embankment, at the top of the slope to protect the system from hammer action. The permit requires the valve anyway due to the high quality watershed. I had planned for the 4" PCV pipe to enter into the center of the field and then branch off in both directions into a series of three parallel pipes approx 300 feet long each and spaced at approximately 20 feet between each pipe. The sprinklers would be evenly spaced along these pipes. The picture is posted at the below link:

I am just confused at how to determine just many sprinklers I am able to use before I do not have enough pressure to operate the system. I would prefer it to be self sufficient, however if I am forced to pump, so be it. I have what I am thinking pictured below. I currently have it pictured using 45 nozzle heads.

So, at this point, how do I determine how many nozzles I can use?

Thanks.

This post has been edited 1 times, last edit by "Wet_Boots" (Mar 22nd 2013, 1:46pm)

45 heads will work fine, even with the 3 gpm nozzle already installed in the Maxipaw, as that will give you about 135 gpm total flow. The 6 gpm nozzles might be too much flow. An in-between nozzle size exists, so that would get you closer to the 200 gpm total flow.

The diagram you posted (I fixed the link {not your fault}) splits into 6 lines, so that works with 2-inch pipe. It doesn't have to be 2-inch all the way to the ends of each line. That's where the friction-loss tables come in.

One more caution to your proposed setup is dealing with inrush flow. Since water seeks its own level, you will have hundreds of feet of empty 4-inch pipe when this starts up. What can sometimes happen is that the air rushes out of of the sprinkler heads far more rapidly than the equal volume of water would, setting up a situation where the water will smash into the system at the speed of the air movement. On the small scale of residential sprinkler systems, this isn't a big concern. On a golf course, it's a different story. One simple way to work with this phenomenon is to have more than one shutoff valve set up in a parallel array, and to open only one valve at a time, until you have full flow. While this complicates the plumbing at the source, it saves you the expense of a 4-inch shutoff valve, and you can go with 1-1/2 inch valves, or maybe 2-inch valves. Smaller valves are easier to operate, too.

{I edited the previous paragraph to remove a reference to a downstream pressure gauge next to the valves, because that wouldn't help with the shutoff valve(s) located way uphill from the sprinklers. (Downstream pressure is a part of the function of the very-expensive specialty valves a golf course would employ to avoid the previously-described damage)}

This post has been edited 1 times, last edit by "Wet_Boots" (Mar 22nd 2013, 6:08pm)